The July heat wave that wilted crops , shriveled rivers and fueled wildfires officially went into the books Wednesday as the hottest single month on record for the continental United States .

The average temperature across the Lower 48 was 77.6 degrees Fahrenheit , 3.3 degrees above the 20th-century average , the National Oceanic and Atmospheric Administration reported . That edged out the previous high mark , set in 1936 , by two-tenths of a degree , NOAA said .

In addition , the seven months of 2012 to date are the warmest of any year on record and were drier than average as well , NOAA said . U.S. forecasters started keeping records in 1895 .

Animated map : U.S. drought in 2012

And the past 12 months have been the warmest of any such period on record , topping a mark set between July 2011 and this past June . Every U.S. state except Washington experienced warmer-than-average temperatures , NOAA reported .

The high temperatures have contributed to a `` rapid expansion '' of drought across the central United States , NOAA found . Dozens of cities and towns already have seen the mercury hit record levels this summer , and three states -- Nebraska , Kansas and Arkansas -- saw record dry conditions between May and July .

That 's battered American farmers ' corn and soybean crops , driven farmers to sell or slaughter cattle they ca n't feed and spurred the U.S. Department of Agriculture to designate more than half of all U.S. counties as disaster zones .

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Past 12 months warmest ever recorded in U.S.

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July 's average U.S. temperature topped 20th-century average by more than 3 degrees

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The first seven months of 2012 are the warmest since record-keeping started in 1895 , NOAA says

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The high temperatures have contributed to a drought that has battered farmers